Fiber optic cable in det cord

ABSTRACT

An apparatus and method for providing a fiber optic cord in a perforating gun.

RELATED APPLICATIONS

This application is the non-provisional of U.S. Provisional ApplicationNo. 62/014,931, filed Jun. 20, 2014.

BACKGROUND OF THE INVENTION

Generally, when completing a subterranean well for the production offluids, minerals, or gases from underground reservoirs, several types oftubulars are placed downhole as part of the drilling, exploration, andcompletions process. These tubulars can include casing, tubing, pipes,liners, and devices conveyed downhole by tubulars of various types. Eachwell is unique, so combinations of different tubulars may be loweredinto a well for a multitude of purposes.

A subsurface or subterranean well transits one or more formations. Theformation is a body of rock or strata that contains one or morecompositions. The formation is treated as a continuous body. Within theformation hydrocarbon deposits may exist. Typically a wellbore will bedrilled from a surface location, placing a hole into a formation ofinterest. Completion equipment will be put into place, including casing,tubing, and other downhole equipment as needed. Perforating the casingand the formation with a perforating gun is a well known method in theart for accessing hydrocarbon deposits within a formation from awellbore.

Explosively perforating the formation using a shaped charge is a widelyknown method for completing an oil well. A shaped charge is a term ofart for a device that when detonated generates a focused explosiveoutput. This is achieved in part by the geometry of the explosive inconjunction with an adjacent liner. Generally, a shaped charge includesa metal case that contains an explosive material with a concave shape,which has a thin metal liner on the inner surface. Many materials areused for the liner; some of the more common metals include brass,copper, tungsten, and lead. When the explosive detonates the liner metalis compressed into a super-heated, super pressurized jet that canpenetrate metal, concrete, and rock.

A perforating gun has a gun body. The gun body typically is composed ofmetal and is cylindrical in shape. Within a typical gun tube is a chargeholder or carrier tube, which is a tube that is designed to hold theactual shaped charges. The charge holder will contain cutouts calledcharge holes where the shaped charges will be placed.

A shaped charge is typically detonated by a booster or primer. Shapedcharges may be detonated by electrical igniters, pressure activatedigniters, or detonating cord. One way to ignite several shaped chargesis to connect a common detonating cord that is placed proximate to theprimer of each shaped charge. The detonating cord is comprised ofmaterial that explodes upon ignition. The energy of the explodingdetonating cord can ignite shaped charges that are properly placedproximate to the detonating cord. Often a series of shaped charges maybe daisy chained together using detonating cord.

In addition to a detonating cord running through the perforating gun, awire may also run through the detonating cord. The wire is used toenable power to the different switch systems. The wires of multipleperforating guns connected together may also be connected. The wire issometimes run to control device on gun string or sometimes it is run toa location at the surface with a controller. Additionally, eachperforating gun may have its own control device for independentactivation.

The problem with the wire is that is has poor reliability due to shockand vibration. Also, the wire may increase inductance that can inhibitcommunication signals along the gun string. This inhibition can limitthe length of the wire, which may limit the depth of the drill string.Furthermore, the wire can suffer from insulation loss. Insulation lossmay result in sparking or arcing between the wire and another conductor.The arcing or sparking may cause pre-detonation of the explosive shapedcharges, detonation cord, or interfere with the electronics generally.Finally, the wire is susceptible to radio frequency (RF) interference.RF interference may cause unintended detonation of the explosives in theperforating gun. As a result, the transportation of loaded perforatingguns maybe made safer by the removal of the wire.

SUMMARY OF EXAMPLES OF THE INVENTION

In this invention a fiber optic cable is used instead of a wire tocommunicate with equipment on the perforating gun. Fiber optics havebeen around for a long time, but they have not been used in downholeperforating guns because of complexity, reliability issues, and thedifficulty of getting a powerful signal to the shaped charges that hasnot been degraded by the Stimulated Brioullin Scattering (SBS) effect.The Stimulated Brioullin Scattering effect causes the transmission ofsignals in a fiber optic cable to scatter and reflect in adverse waysthat negates the ability of a fiber optic cable to transmit enough powerdownhole to cause a detonation. Newer fiber optic cables overcome theseproblems and provide the potential for using a fiber optic over manymiles in length to communicate with a perforating gun located in a harshenvironment. This invention aims to provide a fiber optic cable as aneffective replacement for a wire on a perforating gun.

An example of the invention may include an elongated detonating cordcomprising an explosive encased in a sheath and a fiber optic cable. Thesheath and encased explosives may be substantially cylindrical. Thefiber optic cable may be substantially parallel to the sheath. Theexample may further comprise an optical shield between the fiber opticcable and the explosive. The fiber optic cable may be substantiallycoaxial with the sheath. The fiber optic cable may be affixed to thesheath. The fiber optic cable may be encased by the sheath. The fiberoptic cable may be embedded in the sheath. The fiber optic cable may bespirally wound around the sheath. The fiber optic cable may be offsetfrom the centerline. The fiber optic cable may be single mode ormulti-mode. The fiber optic cable may include one or more optical fibersencased in a shield.

Another example of the invention may include a method of perforating anoil well comprising assembling a string of perforating guns including afiber optic cable, conveying the string of perforating guns into asubterranean well, communicating with the perforating guns using thefiber optic cable. The example may further comprise sending a detonationsignal to the perforating guns using the fiber optic cable anddetonating the perforating guns in response to the detonation signal.The fiber optic cable may be single mode or multi-mode. The fiber opticcable may include one or more optical fibers encased in a shield.

Another example of the invention may include an integrated ballistic andoptic communications cable comprising a tubular sheath, an explosivecontained within the sheath, and a fiber optic cable. The sheath may besubstantially cylindrical. The fiber optic cable may be substantiallyparallel to the sheath. The fiber optic cable may be substantiallycoaxial with the sheath. The fiber optic cable may be affixed to thesheath. The fiber optic cable may be encased by the sheath. The fiberoptic cable may be embedded in the sheath. The fiber optic cable may bespirally wound around the sheath. The fiber optic cable may be offsetfrom the centerline. The example may further comprise an optical shieldbetween the fiber optic cable and the explosive. The fiber optic cablemay be single mode or multi-mode. The fiber optic cable may include oneor more optical fibers encased in a shield.

BRIEF DESCRIPTION OF THE DRAWINGS

For a thorough understanding of the present invention, reference is madeto the following detailed description of the preferred embodiments,taken in conjunction with the accompanying drawings in which referencenumbers designate like or similar elements throughout the severalfigures of the drawing. Briefly:

FIG. 1 is a detonating cord with an internally located coaxial fiberoptic cable.

FIG. 2 is a detonating cord with an internally located off-centeredfiber optic cable.

FIG. 3 is a cross section of a detonating cord with an internallylocated off-centered fiber optic cable.

FIG. 4 is a detonating cord bundled to a fiber optic cord.

FIG. 5 is a charge tube wrapped with a detonating cord bundled to afiber optic cord.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION

In the following description, certain terms have been used for brevity,clarity, and examples. No unnecessary limitations are to be impliedtherefrom and such terms are used for descriptive purposes only and areintended to be broadly construed. The different apparatus, systems andmethod steps described herein may be used alone or in combination withother apparatus, systems and method steps. It is to be expected thatvarious equivalents, alternatives, and modifications are possible withinthe scope of the appended claims.

A typical perforating gun comprises a gun body that houses a chargetube, which further houses the shaped charges. The gun body contains endfittings which secure the charge tube inside the perforating gun. Thecharge tube has charge holes and apex holes for installing shapedcharges. The gun body may have threaded ends that allow it to beconnected to a series of perforating guns or to other downhole tubulars.Typically the detonating cord runs the majority of the length of the gunbody. One or more shaped charges can be placed in the charge tube.Sometimes the shaped charges can all point in the same direction, othertimes some or all may be oriented in different directions about thecenter axis of the charge tube. Different orientations of the shapedcharges may have different angles between each shaped charge. Thedetonating cord wraps around the charge tube to accommodate thedifferent orientations of the shaped charges in phased perforating guns.

The shaped charges include a shaped charge case that holds the energeticmaterial, a liner and an explosive. The shaped charge case typically iscomposed of a high strength metal, such as alloy steel. The liner isusually composed of a powdered metal that is either pressed or stampedinto place. The metals used in liner may include brass, copper,tungsten, and lead.

An example of an embodiment of the invention may include a perforatinggun with a charge tube located within the perforating gun. The chargetube would contain cutouts for each shaped charge. The fiber optic cablemay be adapted to interface with the shaped charges located in thecharge tube. The fiber optic cable may wind around the charge tube suchthat all of the shaped charges are connected to the same fiber opticcable.

The fiber optic cable in this example could terminate at either end ofthe charge tube and interface with another communication device oranother fiber optic cable. The fiber optic could eventually reach thesurface where the operator can control the perforating gun. Theperforating gun could be detonated by sending a signal downhole throughthe fiber optic cable. The detonation command could be achieved by asingle pulse or a series of pulses. The pulses could be used to detonateall the shaped charges, individual shaped charges in a unique sequence,or individual perforating guns.

Referring to FIG. 1, a fiber optic cable 52 is located within adetonating cord 51. Detonating cord 51 includes explosive material 59enclosed in a sheath 58. The fiber optic cable 52 may include one ormore optical fibers 60 encased in a shield 61. The fiber optic cable maybe single mode or multi-mode. In this example the fiber optic cable 52is located substantially centrally within the detonating cord 51. Thefiber optic cable 52 may have one or more Application Specificintegrated Circuit (referred to as “ASIC”) devices 53 attached thatcould be capable of interfacing with a device outside of the detonatingcord 51. The ASIC device 53 may be secured to the fiber optic cable 52by snapping, screwing, adhering to, or press fitting.

In another example, as shown in FIG. 2, the fiber optic cable 52 islocated off-center within the detonating cord 51. Detonating cord 51includes explosive material 59 enclosed in a sheath 58. At one or morelocations along the fiber optic cord 52 there may be an ASIC device 53attached as shown in FIG. 3. In the example shown, a signal could besent or received through the fiber optic cable 52 and that signal couldthen be sent to a device outside of the detonating cord 51. Types ofdevices that could be attached to the ASIC device 53 may includesensors, detonators, switches, or communication devices. In this examplethe ASIC device 53 is configured to allow the fiber optic cable 52 tocommunicate with other electronics outside of the detonating cord sheath58. The fiber optic cable offers the advantage of being radio frequency(RF) interference free as opposed to a conductive wire because a fiberoptic does not transmit electricity, therefore it is considered saferthat a conductor such as a wire.

In another example, as shown in FIG. 4, the fiber optic cable 52 isaffixed to the outside of a detonating cord 51 to make an integratedcommunications cable 55. The fiber optic cable 52 is bundled to thedetonating cord 51 using a fastening device 54. The fastening device 54shown is a tie that wraps around both the fiber optic cable 52 and thedetonating cord 51. The fastening device 54 may be a metal or plastictie, a cable, a wire, u-bolt, a ring, additional sheath, tape, heatshrink, tubing, conduit, adhesive or a similar fastening mechanism.

The integrated communications cable 55 may then be wrapped around acharge tube 57 as shown in FIG. 5. A charge tube 57 holds shaped chargesand is then placed inside a perforating gun. In a typical perforatingjob, shaped charges may be lined up along the charge tube 57 allpointing the same direction, which is referred to as zero phase. Theshaped charges may be offset from each other by rotating a certainnumber of degrees about the center of the charge tube 57 from one shapedcharge to the next. The offset angle is referred to as the phase angle.Because the charges are often offset from each other and thereforepointing in different directions, the integrated communications cable 55has to wrap around the gun such that the detonating cord 51 and thefiber optic cable 52 may interface with each and every shaped chargesapex. The shaped charge apex may have additional equipment or devicesattached to it. Generally the shaped charge apex will be located at anapex hole on the shaped charge.

In the example of FIG. 5, the integrated communications cable 55 may beattached to the charge tube 57 using a variety of fastening devices 54including ties, wires, cables, rings, u-bolts, or similar fasteningmechanisms. Further, the fiber optic cord 52 may be individually securedto the charge tube 57 using a variety of fastening devices 56 includingmetal or plastic tie, a cable, a wire, a ring, additional sheath, tape,heat shrink, tubing, u-bolts, conduit, adhesive or a similar fasteningmechanism. The integrated communications cable 55 may also be fastenedto the shaped charges directly.

Although the invention has been described in terms of particularembodiments which are set forth in detail, it should be understood thatthis is by illustration only and that the invention is not necessarilylimited thereto. Alternative embodiments and operating techniques willbecome apparent to those of ordinary skill in the art in view of thepresent disclosure. Accordingly, modifications of the invention arecontemplated which may be made without departing from the spirit of theclaimed invention.

What is claimed is:
 1. An elongated detonating cord comprising: anexplosive encased in a sheath; a fiber optic cable.
 2. The detonatingcord of claim 1 wherein the sheath and encased explosives aresubstantially cylindrical.
 3. The detonating cord of claim 1 wherein thefiber optic cable is substantially parallel to the sheath.
 4. Thedetonating cord of claim 1 further comprising an optical shield betweenthe fiber optic cable and the explosive.
 5. The detonating cord of claim3 wherein the fiber optic cable is substantially coaxial with thesheath.
 6. The detonating cord of claim 3 wherein the fiber optic cableis affixed to the sheath.
 7. The detonating cord of claim 3 wherein thefiber optic cable is encased by the sheath.
 8. The detonating cord ofclaim 3 wherein the fiber optic cable is embedded in the sheath.
 9. Thedetonating cord of claim 3 wherein the fiber optic cable is spirallywound around the sheath.
 10. The detonating cord of claim 7 wherein thefiber optic cable is offset from a centerline of the sheath.
 11. Amethod of perforating an oil well comprising: assembling a string ofperforating guns including a fiber optic cable; conveying the string ofperforating guns into a subterranean well; communicating with theperforating guns using the fiber optic cable.
 12. The method of claim 11further comprising: sending a detonation signal to the perforating gunsusing the fiber optic cable; detonating the perforating guns in responseto the detonation signal.
 13. An integrated ballistic and opticcommunications cable comprising: a tubular sheath; an explosivecontained within the sheath; a fiber optic cable.
 14. The integratedballistic and optic communications cable of claim 13 wherein the sheathis substantially cylindrical.
 15. The integrated ballistic and opticcommunications cable of claim 13 wherein the fiber optic cable issubstantially parallel to the sheath.
 16. The integrated ballistic andoptic communications cable of claim 13 wherein the fiber optic cable issubstantially coaxial with the sheath.
 17. The integrated ballistic andoptic communications cable of claim 13 wherein the fiber optic cable isaffixed to the sheath.
 18. The integrated ballistic and opticcommunications cable of claim 13 wherein the fiber optic cable isencased by the sheath.
 19. The integrated ballistic and opticcommunications cable of claim 13 wherein the fiber optic cable isembedded in the sheath.
 20. The integrated ballistic and opticcommunications cable of claim 13 wherein the fiber optic cable isspirally wound around the sheath.
 21. The integrated ballistic and opticcommunications cable of claim 18 wherein the fiber optic cable is offsetfrom a centerline of the sheath.
 22. The integrated ballistic and opticcommunications cable of claim 13 further comprising an optical shieldbetween the fiber optic cable and the explosive.
 23. The integratedballistic and optic communications cable of claim 13 wherein the fiberoptic cable is a single mode fiber optic cable.
 24. The integratedballistic and optic communications cable of claim 13 wherein the fiberoptic cable is a multi-mode fiber optic cable.